Closed-loop control in silver recycling

April 8, 2016

United DMS makes use of an integrated diaphragm pump and controller combination.

When a company recycles and refines more than 25 million pounds of silver-bearing material each year, equipment reliability is a must. Recently, one of the largest silver-bearing film recyclers found a better way, with closed-loop control, to move and manage fluids used in silver recovery.

It takes precise fluid dosing and pump reliability to keep this process moving, but existing equipment’s poor reliability was affecting the chemical washing efficiency at United DMS. A 1-inch ARO electronic interface diaphragm pump replaced the equipment along with a controller equipped with a flow meter to automatically meter fluids and prevent overfilling. This change eliminated reliability issues and related downtime, and overall pump productivity jumped by more than 75 percent, according to T. J. Harris, maintenance manager at United DMS.

The ARO Controller precisely controls the transfer of material from the ARO EXP Series Electronic Interface Diaphragm Pump to the day tanks at the United DMS plant.

A closed-loop controller with remote operating capabilities offers dispensing repeatability within 1 percent with less operator oversight. The controller solution supports a safety focus, meets compliance requirements, streamlines processes, lowers cost and allows customized production lines.    

Headquartered in Knoxville, Tennessee, United DMS is the nation’s largest silver-bearing film recycler. Its 100,000-square-foot, three-facility operation covers more than 25 acres of film warehousing, sorting, grinding, washing and smelting services. Work performed there helps avoid discarding millions of pounds of plastic and precious metals into landfills and generates raw materials used in new products.

Process description

Recycling silver-bearing film involves steps ranging from the receipt, shredding and assessment of materials to specialized washing processes. Smelting restores the silver to a purity of 99.9 percent. Plastic base films are also recycled as raw materials for new commercial plastics.

To facilitate removing silver from various films, base materials are treated and then separated from a silver emulsion mix. They are then pumped into 12,000-gallon settling tanks for further processing. Chemicals are added to maintain pH balance, followed by polymers to precipitate the silver. This critical process step turns the emulsion water into reusable silver. At this point, a reliable pump and controller must accurately dispense and track chemical flow into the settling tanks.

While the company typically processed up to 300,000 gallons of emulsion mix each week, the existing diaphragm pump and batch control system limited its full production potential. The demanding environment resulted in downtime for pump disassembly, repair, reassembly and restart, while issues with the controller’s circuit board often led to a failure to signal the pump to cycle.     

The ongoing equipment issues led to manual dispensing of the chemical solution, taking the operator away from the settling tanks to a remote area. There, fluid media was added based on a counting formula. This workaround had negative impacts on material use, inventory management and worker safety. Unanticipated delays and costs led to recalibrating the emulsion mix if an operator exceeded the pH level.

"Compared to the original industrial pump installed, the replacement pump offered the reliable dosing needed while allowing them to verify how much media was dispensed for material tracking purposes," said James Herbers, sales manager for Fluid Management.   

Equipment replacement

The key to this phase of United’s operation is pump reliability, according to Blake Brown, production supervisor at United DMS. "The new ARO system installed easily into our current layout, which meant we could address specific performance issues without having to reconfigure any of our existing piping," he said.

This is the first fully closed-loop controller for air-operated diaphragm pumps that allows operators to customize production lines and remote monitor fluid transfers without manual intervention, according to ARO. The result is greater efficiency and accuracy in fluid delivery and less overall downtime. With touch-and-walk-away automation, users are assured dispensing repeatability within 1 percent.

In the final step of the process, another ARO EXP Series Electronic Interface Diaphragm Pump transfers acid to the material in order to extract the silver.

"Not only has the pump and controller improved our bulk transfer and mixing process, [but] it also supports worker safety by eliminating the need for manual operator dispensing," said Gerry Fishbeck, president of United DMS. "All around, it’s proven to be the best pump system we’ve got, which is why we ordered two more systems for our bulk caustic tank and caustic day tank transfer processing areas.”

United DMS now has a fully automated, multi-pump system for batching and tank filling with plus or minus one-percent repeatability. Remote capabilities free workers from "pump duty."

Productivity impact

By replacing the existing pump and controller, the company was able to minimize downtime, streamline processes, save money and reduce its total cost of ownership.

More than eight months after installation the system was still delivering results. The company consistently meets its ideal pH balance for emulsion mix processing with no further liquid dispensing or mixing issues. After working through a number of failed alternatives, staff said they are pleased with the installed system’s simplicity and reliability. This is largely because the electronic interface diaphragm pump provides all the benefits of an air-operated pump with the controllability of an electric pump.

Internal cycle counter and end-of-stroke pressure signals track feedback and pump data. Its convoluted diaphragm lasts up to four times longer than traditional diaphragms. The leak detection option detects and notifies of diaphragm failure. The controller remotely monitors and manages leak detection, liquid-level sensing and proportional control, offering multi-pump control for accurate two-part batching. The lube-free design has fewer parts for easy maintenance and repair, and it is ATEX-compliant including all voltage options for safety assurance. Remote triggers and alerts send timely operating data.

Anatomy of a control function

Its developers said the ARO controller responds to user needs for a closed-loop system that allows production line customization and remote monitoring of fluid transfer. It solves fluid management issues and easily integrates into existing production lines.

Traditional control systems rely on manual processes that require the attention of an operator or multiple operators. A closed-loop controller allows remote control of batching and monitoring fluid transfer with an ease of use that reduces errors and lowers costs. An operator does not have to be stationed at each pump as it draws and dispenses into another location.

The controller determines if the required flow rate can be maintained or not. If the flow rate cannot be maintained, an alarm alerts operators.

The dual-pump controller’s remote triggers perform auto shutdowns and display critical operating data and service alerts via a control-panel display. As a closed-loop system, the controller features touch-and-walk-away automation that achieves dispensing repeatability within 1 percent.

The controller constitutes a closed-loop system with the air-operated diaphragm pumps it is connected to. The controller sends signals to a pump to maintain pump speed and volume delivery. Sensors in the pump relay signals back to the controller, which are used to adjust the outgoing signal’s rate and maintain programmed parameters.

Additionally, the controller monitors other signals, including leak detectors, analog signals and remote commands. For example, these alert the operator so they know when a diaphragm has ruptured.

The multi-pump controller includes auto-fill functionality that receives signals from level sensors installed in a container, allowing the pump to maintain a consistent fluid level in the tank.

Leak-detector sensors use optical technology embedded in the pump’s air chambers to detect when liquid is present where it should not be. The sensor prism refracts light when fluid enters the space, and signals the controller to alert the operator.

When a pump loses its prime, it stops pumping fluid and starts pumping air, at which point the controller signals the operator to stop the pump.

Two pumps can be managed with a single controller. The pumps can mirror one another or complement each other. The controller uses a proprietary algorithm to monitor stroke timing and determine whether the pump is running at the programmed speed.

Applications include tank filling, repackaging, blending, dewatering, pipe flushing, dispensing, fluid transfer, cleaning and batching.

Mark Jermeay is a product leader for fluid management at ARO, a brand of Ingersoll Rand. Ingersoll Rand creates comfortable, sustainable and efficient environments.

Sponsored Recommendations

Choosing The Right Partner for CHIPS Act Investments

As the U.S. looks to invest in the semiconductor research and production using CHIPS Act 2022 funding, it's important to choose the right partner.

EMWD Uses Technology to Meet Sustainability Goals

Eastern Municipal Water District pilots artificial intelligence-enabled control and machine learning to help save energy, reduce costs, and improve quality.

Protein Processing Solutions: Automation & Control

For protein processors looking to address industry challenges, improve efficiency, and stay ahead in a competitive market, Rockwell Automation offers tailored automation, control...

Automotive Manufacturing Innovation: Smart Solutions for a Connected Future

Rockwell Automation provides automation and control systems tailored for the automotive and tire industries, supporting electric vehicle production, tire production, battery production...